The present invention relates to a hinge mechanism for variable displacement compressors used in, for example, automobile air-conditioners.
A typical variable displacement compressor has a housing, which houses a crank chamber, and a cylinder block. A drive shaft extends through the crank chamber. Cylinder bores extending through the cylinder block accommodate pistons. A lug plate is fixed to the drive shaft to rotate integrally with the drive shaft. A swash plate, which drives the pistons, is located adjacent to the lug plate.
The lug plate is connected to the swash plate by a hinge mechanism. Each piston is coupled to the swash plate. In this structure, the difference between the pressure of the crank chamber and the pressure of the cylinder bores is altered by adjusting the size of the opening in a displacement control valve. The inclination of the swash plate changes in accordance with the pressure difference, the displacement of the compressor varies accordingly.
With reference to FIG. 4, a hinge mechanism 51, which enables a swash plate 54 to incline, includes a guide bore 53 formed on a rear surface 52a of a lug plate 52 and a pin 55 projecting from a front surface of the swash plate 54. The guide bore 53 is formed so that its axis AXg is inclined relative to the rear surface of the lug plate 52. The pin 55 has a spherical end portion 55a, which is received by the guide bore 53 and which slides along the guide bore 53 in the direction of the guide bore axis AXg.
When the compressor is operated, a compression load acts on the pin 55. This applies a bending moment M to a proximal end 55b of the pin 55. The bending moment M is calculated from equation (1).
M=Faxc2x7L=Fbxc2x7cos xcex8xc2x7Lxe2x80x83xe2x80x83(1)
In the equation, Fa represents the force applied to the spherical portion 55a of the pin 55 by the compression load in a direction perpendicular to the pin axis AXp. Fb represents the force applied to the spherical portion 55a by the compression load in a direction perpendicular to the guide bore axis AXg. The symbol L represents the length of the pin 55 extending from the swash plate 54, and xcex8 represents the angle between the pin axis AXp and the guide bore axis AXg. The angle xcex8 is equivalent to the angle formed between the two forces Fa, Fb.
The length L of the pin 55 must be relatively long so that the pin 55 can move in the guide bore 53 for a distance that enables the swash plate 54 to move between a maximum inclination position and a minimum inclination position. Further, the angle xcex8 between the pin axis AXp and the guide bore axis AXg must be minimized to avoid interference between the guide bore 53 and the pin 55. This results in a large force Fa being applied to the spherical portion 55a of the pin 55 by the compression load.
In the structure of FIG. 4, the bending moment M applied to the proximal end 55b of the pin 55 is large. Therefore, the pin 55 must be securely fixed to the swash plate 54 by press-fitting the proximal end 55b of the pin 55 into a retaining bore 54a of the swash plate 54. Therefore, the dimensions of the proximal end 55b and the retaining bore 54a must be accurate. Further, the diameter and length of the press-fitted portion including the proximal end 55b must be as large as possible. This enlarges the pin 55 and its surrounding components. As a result, the manufacturing cost increases, and the weight of the compressor increases.
Japanese Unexamined Patent Publication No. 10-54353 proposes a compressor in which the pin is located on the lug plate and received by a guide groove in the swash plate. The guide groove extends diagonally relative to the front surface of the swash plate. The pin slides in the axial direction of the guide groove, and the axes of the pin and guide groove intersect.
However, the guide groove must be long to enable the pin to slide between locations corresponding to the swash plate""s maximum inclination position (where the displacement of the compressor is maximal) and minimum inclination position (where the displacement of the compressor is minimal). Thus, a large support must be provided on the front surface of the swash plate to form the guide groove. This increases the weight of the swash plate. In addition, the large support may cause a weight imbalance of the swash plate. This would result in inaccurate positioning, or inclination, of the swash plate when the displacement control valve alters the pressure difference between the crank chamber and the cylinder bores.
Furthermore, the pin extends from the rear surface of the lug plate toward a location on the swash plate corresponding to the top dead center position of the pistons. The angle of the pin relative to the drive shaft is always the same regardless of the compressor displacement. Thus, the bending moment at the proximal end of the pin increases as the compressor displacement increases.
It is an object of the present invention to provide a light and inexpensive variable displacement compressor that ensures satisfactory response to displacement control and simplifies the structure for fixing the pin to a drive plate. To achieve the above object, the present invention provides a variable displacement compressor having a crank chamber and a cylinder bore within a housing, a drive shaft extending through the crank chamber, a lug plate integrally attached to the drive shaft, and a drive plate located adjacent to the lug plate. The drive plate is coupled to the lug plate by a hinge mechanism. The hinge mechanism drives the drive plate and permits the drive plate to rotate with and incline with respect to the drive shaft. The displacement of the compressor varies according to the inclination of the drive plate based on a pressure difference between the crank chamber and the cylinder bore. A guide is provided on the lug plate. The guide has an axis. A pin projects from the drive plate toward the lug plate. The pin engages and is guided by the guide. The pin has an axis. The axis of the guide extends in a direction intersecting the axis of the pin
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.